1. Field of the Invention
The present invention relates to an outboard motor having a case that forms an outer shell of the outboard motor. More specifically, the present invention relates to an outboard motor in which the case comprises an extrusion.
2. Description of the Related Art
Typical outboard motors include an internal combustion engine adapted to drive a driveshaft, which in turn drives a propeller shaft. The engine usually is enclosed within a cowling, and a casing generally encloses the driveshaft and propeller shaft. The casing typically includes an upper case that is generally vertically-directed so as to generally enclose the driveshaft. A lower case generally encloses the propeller shaft, and often encloses gearing through which the driveshaft and propeller shaft communicate.
An example outboard motor is disclosed in Japanese Patent Document JP-A-Hei 8-34394. In this publication, the outboard motor includes a casing having a generally vertically-extending upper case. A driveshaft is contained in an internal space defined within the upper case. In the illustrated embodiment, the upper case is formed by casting a metal, and has a relatively complex, curved shape. A lower case generally contains the propeller shaft, and is also formed by casting a metal.
Components such as the upper and lower cases tend to be heavy. Also, casting metal can be a cumbersome process. Thus, typical upper cases formed by casting metal tend to be heavy and cumbersome to manufacture.
Further, typical outboard motors employ water-cooled engines. In such motors, water from below the surface is used as cooling water. Such cooling water is typically drawn into the lower case and then directed through a water passage formed in the internal space of the upper/lower cases to be supplied to the engine for cooling purposes. The water passage typically increases a cross-section of the case. Such a large-cross-section case tends to create a significant propulsion resistance for the associated boat.